[ntp:questions] Stratum goes back to 16 all the time

Danny Mayer mayer at ntp.isc.org
Sat Dec 30 20:40:03 UTC 2006


Tom Smith wrote:
> independence at blinkenlights.se wrote:
>> Hi, I've set up a ntpd on my linux box and at first it worked fine and
>> got a stratum of 2 after a while. Then, after a couple of minutes, it
>> got a stratum of 16 again. Now it hops back and forth and doesn't seem
>> to be very stable at all.
>> I sat and watched the output from peers in ntpq for a while, and first
>> everything is fine but after a while all the remote servers get *+- etc
>> in front of their names, I've tried to read what these mean but I'm
>> don't really understand.
>>
>> Here's the output from ntpq peers:
>> ntpq> peers
>>      remote           refid      st t when poll reach   delay   offset
>> jitter
>> ==============================================================================
>>  nissan.ifm.liu. .GPS.            1 u   16   64   17   27.721  -479.06
>> 115.831
>>  timmy.lysator.l .GPS.            1 u   28   64   17   28.089  -380.49
>> 72.967
>>  timehost.lysato .GPS.            1 u   40   64   17   28.833  -462.36
>> 111.578
>>  Time1.Stupi.SE  .PPS.            1 u   23   64   17   24.651  -313.99
>> 115.770
>>  ntp1.sth.netnod .PPS.            1 u   28   64   17   26.199  -475.23
>> 119.470
>>  ntp2.gbg.netnod .PPS.            1 u   51   64   17   32.007  -455.40
>> 123.874
>  >    .
>  >    .
>  >    .
>> ntpq> peers
>>      remote           refid      st t when poll reach   delay   offset
>> jitter
>> ==============================================================================
>>  nissan.ifm.liu. .GPS.            1 u  112   64   36   27.721  -479.06
>> 115.831
>> *timmy.lysator.l .GPS.            1 u   58   64   37   28.089  -380.49
>> 118.008
>> +timehost.lysato .GPS.            1 u    8   64   77   27.253  -522.91
>> 141.296
>> -Time1.Stupi.SE  .PPS.            1 u   53   64   37   24.651  -313.99
>> 169.327
>> +ntp1.sth.netnod .PPS.            1 u   58   64   37   26.199  -475.23
>> 116.326
>> +ntp2.gbg.netnod .PPS.            1 u   15   64   77   31.388  -633.99
>> 250.372
>>
>> Why might does this happen?
>>
>> ntptrace shows this:
>> localhost: stratum 16, offset 0.000000, synch distance 0.010290
>>
> 
> You are starting with an offset of almost 1/2 second from your
> sources. After 5 polls of the sources, your client selects a set
> of servers to use as a reference. Those are the "*" and "+"
> characters that appear in the first column. The "-" character
> indicates a source that was rejected for one reason or another.
> The source with an "*" is the "synchronization source".
> 
> After a period of time during which the consensus offset is
> deemed to be stable, the client will reset its clock to
> try to bring the offset to 0. When this happens, the client
> stratum goes back to 16 (unsynchronized) until it synchronizes
> again. The same synchronization sequence then repeats
> indefinitely.
> 
> You should expect this to happen repeatedly for several
> hours or even for a day or 2 until your client computes its
> characteristic drift rate and is able to cruise along
> between polls at approximately the same rate as the
> clocks you are using as sources.
> 
> You can accelerate the process as follows:
> 
> 1) Stop ntpd
> 2) Add "iburst" to the end of each of your server lines in ntp.conf
> 3) make sure you have a (valid) driftfile declaration in ntp.conf
> 4) Delete any existing ntp.drift file
> 5) Use "ntpdate -b [server]" to set your clock to the
>     correct time. This should be part of your boot or ntpd start sequence.
>     It is configured differently for different Linux distributions.
>     Red Hat, for example, uses the file /etc/ntp/step-tickers to list
>     the servers that ntpdate should use on initial startup.

Skip this step. Use ntpd -g instead when starting ntpd. This will set
the clock even if it's way off.

> 6) Start ntpd.
> 7) Let ntpd run for at least a day without disturbing it
> 
> -Tom
> 
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